Estimation of electric charge distribution in thundercloud by using the inverse approaches

地面电场强度信息对雷电预报有一定的参考价值。为了考察所提出的方法从电场信息估计雷暴云中电荷分布的能力，进行了以下研究：首先，提出了一种新的边界元方法--半无限边界元法来计算云中电荷引起的电场。其次，研究了由地面电场测量值估计电荷分布的牛顿法、最小二乘法、抽样模式匹配法、神经网络和卡尔曼滤波等算法。在电荷估计问题中，测点的数目可能很少，必须引入特殊的装置来增加“虚拟测点”。数值模拟结果表明，牛顿法是最适合于精确估计的方法，而且估计时必须测量三位有效数字的电场强度数据。作为另一项研究，研制了一种使用电位器的耐候型地面电场测量装置。然而，质量的测量精度必须提高，以实际使用。

The information of the electric field intensity on the ground is useful for forecasting the lightning. To investigate the capability of the proposed approaches for estimating the electric charge distribution in thundercloud from the electric field information, the following studies were carried out.First, a new boundary element technique named semi-infinit boundary element was proposed to calculate the electric field caused by the electric charge in cloud. It is found that the electric field distribution considering the effect of the topography can easily be evaluated by using the technique.Second, to estimate the electric charge distribution from the electric field measured on the ground surface, some algorithms such as Newton scheme, Least square's method, Sampled pattern matching method, Neural network and Kalman filter were investigated. In the electric charge estimation problem, the number of the measuring points may be so small that a special device must be introduced to increase the "virtual measuring point". It is found from the numerical simulation that Newton scheme would be most suitable for accurate estimation, and also the electric field intensity data must be measured with three significant digit figures for the estimation.As another study, a weather-proof type equipment using potentiometer was developed to measure the electric field on the ground. However, the quality of the measurement accuracy must be improved for practical use.